Turtle Observer Program Report 2018: Marin Municipal Water District
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Turtle Observer Program Report 2018:
Biological survey results and community science strategies
Marin Municipal Water District
Gabriela Guaiumi, Watershed Stewards Program Member
Eric Ettlinger, Aquatic Ecologist
2018
Introduction
The western pond turtle (Actinemys spp.) is the only native aquatic turtle in California, and was recently
split into two different species: the northern western pond turtle (Actinemys marmorata) and the
southern western pond turtle (Actinemys pallida) (Nafis 2018a). Their ranges meet at the Golden Gate.
Years of habitat degradation and invasive competition have reduced western pond turtle populations to
a critical level. The International Union for the Conservation of Nature (IUCN) lists the western pond
turtle as ‘Vulnerable’ (IUCN, 2016), and the California Department of Fish and Wildlife lists it as a
“species of special concern.” Populations in the San Francisco Bay Area have struggled, but effective
management strategies can allow this species to persist in tandem with human use of its habitat.
Persistent western pond turtle populations exist in Marin Municipal Water District’s (MMWD) reservoirs
in Marin County, California. Due to the proximity to suburban areas, pet releases are common and non-
native turtle species are in the majority throughout the watershed (MMWD, 2017). The Water District’s
Aquatic Ecologist and Watershed Volunteer Coordinator have developed an observational survey
designed to provide the District with an annual snapshot of the population dynamics in four reservoirs.
The survey is designed with community science in mind - dedicated volunteers provide hours of
monitoring that would not be possible otherwise. The goals for the 2018 observer program were two-
fold: 1) to establish population estimates for native and non-native turtles in each reservoir and
determine the proportion of native to non-native turtles and 2) to educate the public about native turtle
species and the importance of not releasing pets into the wild.
1
Methods
On February 24th 2018, community scientists attended a three-hour lesson covering the observational
survey techniques, turtle species identification, and methods for public engagement. The identification
techniques were taught using photos of western pond turtles (WPT) and red-eared sliders, as well as a
live slider to show distinguishing field markings. One of MMWD’s rangers came to address our
volunteers about interactions with watershed visitors and appropriate public engagement.
Our volunteers were invited to observe at any survey site at any time between February 24th and June
4th. One of our most seasoned volunteers began observing January 28th and collected six days of data
prior to the training.
MMWD provided all equipment necessary for the surveys, including binoculars and spotting scopes, and
provided training on the use of the optics during the orientation on February 24th. The Watershed
Stewards Program (WSP) Member assisting with the program curated and logged the data forms
submitted by volunteers into Excel, and performed quality assurance by altering species identifications
where necessary.
Surveys occurred at one or more of four locations on MMWD’s reservoirs – Alpine Lake (ALP), Bullfrog
Trail (BFT), Phoenix Lake (PHX), and Lake Lagunitas (LAG). Each site was chosen due to previous years’
success in observational surveys, but participants were also encouraged to scout out new areas. Surveys
lasted between 0.25 and 5.5 hours, and observations recorded at the same location on the same date
were reduced to only the high count of each species for the day. Populations were estimated using the
high count for each site.
Observations were recorded on a paper data sheet which included the volunteer name, date, time
interval, and weather. Volunteers were asked to record qualitative observations for each turtle
including: the observing location, whether the turtle was basking or swimming, if the head was visible, if
the turtle had a red stripe behind the eye, if the turtle had yellow facial stripes, if the throat was
noticeably lighter than the face, and if there were yellow markings on the shell. Based upon these
observations, volunteers could then classify the turtle as a western pond turtle (AM), red-eared slider
(TS), unidentified non-native (NN), or an unknown species (U). WSP Members were also able to use this
information to identify species classification errors when doing quality assurance.
Results
Total Actinemys Marmorata (AM) and Non-Native (NN) Turtles in MMWD Reservoirs
200
High Count ofTurtles
150
100
50
0
AM NN AM NN AM NN AM NN AM NN AM NN AM NN AM NN AM NN AM NN AM NN
2003 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018
2Bullfrog Trail
Volunteers conducted 25 observational surveys at Bullfrog Trail through the 2018 season and observed
11 western pond turtles (AM) and 88 non-native turtles (NN) at the highest count. The peak date for
basking was April 14th.
Alpine Lake
Volunteers conducted 15 observational surveys at Alpine Lake below Bon Tempe Dam through the 2018
season. Volunteers observed 13 western pond turtles (AM) and 53 non-native turtles (NN) at the highest
count. The peak date for basking was March 11th.
Lake Lagunitas
Volunteers conducted eight observational surveys at Lake Lagunitas through the 2018 season.
Volunteers observed six western pond turtles (AM) and 13 non-native turtles (NN) at the highest count.
The peak date for basking was April 14th.
Phoenix Lake
Volunteers conducted 11 observational surveys at Phoenix Lake through the 2018 season. Volunteers
observed six western pond turtles (AM) and 26 non-native turtles (NN) at the highest count. The peak
date for basking was March 31st.
Total Population Composition
Mt. Tam Watershed Populations at all Survey Sites
17%
Unknown
14%
Western pond turtle
69%
Non-native
There were 44 unknown observations, and almost half of those were from Bullfrog Trail. Unknown
species accounted for 17% of the total observations, western pond turtles accounted for 14%, and non-
native turtles accounted for the other 69%.
The 2018 population estimates for all lakes, based on single-day high counts, were 36 western pond
turtles (up from 25 individuals in 2017) and 180 non-native turtles (up from 112 individuals in 2017).
3Peak Basking Dates
Bullfrog Trail Lake Lagunitas
4-Jun 4-Jun
15-May 15-May
25-Apr 25-Apr
5-Apr 5-Apr
16-Mar 16-Mar
24-Feb
24-Feb
4-Feb
4-Feb
2010
2011
2012
2013
2014
2015
2016
2017
2018
2010
2011
2012
2013
2014
2015
2016
2017
2018
Alpine Lake Phoenix Lake
4-Jun 4-Jun
15-May 15-May
25-Apr 25-Apr
5-Apr 5-Apr
16-Mar 16-Mar
24-Feb 24-Feb
4-Feb 4-Feb
2010
2011
2012
2013
2014
2015
2016
2017
2018
2012
2013
2014
2015
2016
2017
2018
Over the course of all turtle observer seasons, basking peaks at the four sites have ranged between
February 2nd and May 29th. Peak basking dates appear to be shifting earlier at Alpine and Phoenix Lakes,
but no trend has been seen at Bullfrog Trail or Lake Lagunitas.
Volunteer Statistics
MMWD’s Turtle Observer Program orientation/training was attended by 36 individuals, 21 of whom
provided survey data during the season. Four of those volunteers were return volunteers. Surveys were
conducted on 30 of the 101 total available days between February 24th and June 4th. An additional six
surveys were provided by Kathy Tama from January 28th to February 10th. Volunteers contributed a total
of 80 survey hours over 57 surveys. Volunteers made 1373 individual turtle observations.
4Volunteer Effort by Year
40
35
30
# of Volunteers
25
20
15
# of Volunteers Trained
10
# of Volunteers who Participated
5
0
2010 2011 2012 2013 2014 2015 2016 2017 2018
Total number of observation visits
140
131
120
100
80 70 66 66
63
57
60 45
37 42
40
20
0
2010 2011 2012 2013 2014 2015 2016 2017 2018
Total volunteer observation hours
280
251
240
200
160 135
120 106
91 84 85 80
76
80 63
40
0
2010 2011 2012 2013 2014 2015 2016 2017 2018
5Discussion
The 2018 Turtle Observer season was successful in providing a snapshot of the population dynamics
between native and non-native residents on the Mount Tamalpais Watershed. The number of non-
native turtles observed this year was the highest recorded on our watershed, with non-native turtles
outnumbering our native western pond turtles (WPT) by more than 4:1. The non-native population also
appears to be increasing at a faster rate, which supports the fact that WPTs have a lower recruitment
than the non-native turtles. Red-eared sliders reach sexual maturity at a younger age than WPT and
have higher fecundity, so this trend is likely to continue if there is no intervention.
Both native and non-native turtles are utilizing the same basking sites, egg laying sites and food sources.
There is concern that as the non-native population continues to increase, competitive displacement of
our native WPT could occur. While reducing the population of non-native turtles through the use of
trapping has been a goal in past years, there were no efforts made to trap turtles this year. There were
18 red-eared sliders that were passively captured and brought to a local reptile rescue.
One recommendation to increase numbers of native turtles is to engage with the Western Pond Turtle
Head-start program created by the Oakland Zoo, San Francisco Zoo, and Sonoma State. WPT eggs are
collected from native populations, the hatchlings are reared at the zoo until they are large enough to
better avoid predation (one year old zoo-reared turtles are the size of three or four year old wild
turtles), and then they are released back into the wild. Entering into a partnership with these agencies
could increase native turtle population numbers at a greater rate than would occur naturally. This, in
tandem with invasive turtle removal efforts, could help native turtles become the majority in the future.
Community Science: Training, Statistics and Strategies
The continuation of this program is completely dependent on our community scientists who volunteer
their time. Based on the range of dates for peak turtle observations, it is recommended that Turtle
Observer Training take place in mid to late January. At the latest, training should take place in early
February. The number of participating volunteers remained about the same in 2017 and 2018, but the
number of observation visits and hours observed decreased. Only 60% of the volunteers trained actually
went out to observe, but that percentage appears to be the norm every year.
Some of the data sheets turned in were missing information or were confusing to interpret. This can be
attributed to not explicitly showing volunteers how to fill out the data sheet during training. It would be
beneficial to do this in next year’s training to avoid confusing or incomplete data sheets in the future. If
the data sheets had been processed and entered at the beginning of the season instead of the end, this
issue could also have been potentially mitigated.
Increasing volunteer hours and improving the cohesiveness of the program could be achieved by hosting
small group observation days. Utilizing the Volunteer Program’s outreach sources or a site such as
Meetup could accomplish this. Offering small prizes when certain thresholds are met (for example – a
volunteer shirt on your first observation day, a cool sticker after doing two hours of survey, etc.) could
also improve participation. In addition, Turtle Tuesday emails could be sent out every other week and a
fun, informational graphic or video could be sent out on alternating weeks to keep volunteers engaged.
6Important considerations for future years include determining the minimum number of hours or
individual observations necessary for accurate population estimation and predicting the best dates to
conduct surveys through the analysis of past high count dates and historical weather data. By reducing
the number of variables present, more statistically significant results could be generated.
References
Garcia and Associates (GANDA). 2003. Mt. Tamalpais Watershed Western Pond Turtle Study. Prepared
for Marin Municipal Water District.
Hosfield, D., and E. Ettlinger. 2016. Turtle Observer Program Report. August 2016. Marin Municipal
Water District.
Nafis, G. 2018a. California Herps - A Guide to the Amphibians and Reptiles of California. (25 June 2018.)
http://www.californiaherps.com/ “Northwestern Pond Turtle - Actinemys marmorata."
< http://www.californiaherps.com/turtles/pages/a.marmorata.html>
Nafis, G. 2018b. California Herps - A Guide to the Amphibians and Reptiles of California. (25 June 2018.)
http://www.californiaherps.com/ “Red-eared Slider - Trachemys scripta elegans."
< http://www.californiaherps.com/turtles/pages/t.s.elegans.html>
Oakland Zoo. (June 25 2018) http://www.oaklandzoo.org/
<
http://www.oaklandzoo.org/conservation-partners/western-pond-turtle>
Washington Department of Wildlife. 1993. Status of the western pond turtle (C/emmys mannorata) in
Washington. Unpub. Rep. Wash. Dept. Wild., Olympia.
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